Design method of free-form optical device for indirect lighting of LED on top of vehicle cabin

Abstract

The application provides a design method of a free-form optical device for indirect lighting of a LED on a top of a carriage, comprising: obtaining a lighting angle range and an installation position of the LED, so as to analyze a light attenuation gradient distribution of the LED light source at different positions on the top of the carriage; obtaining a Euclidean distance of two LED light sources at opposite positions, combining the light attenuation gradient distribution to analyze a light uniformity of the lighting on the top of the carriage; determining a target uniformity according to a preset lighting uniformity standard, obtaining a uniformity difference between the target uniformity and the light uniformity, when the uniformity difference is greater than a preset uniformity threshold, reversely calculating a reflection angle required by an outgoing light ray of the LED corresponding to each preset sampling point on the top of the carriage based on the target uniformity and the light attenuation gradient distribution, so as to design a reflection surface or a total reflection surface of the free-form optical device. The corresponding free-form optical device is designed through the reflection angle, so as to overcome the problems of poor lighting uniformity and low light efficiency utilization in the prior art.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of optical devices, in particular to a design method of a free-form surface optical device for LED indirect lighting on a carriage roof. BACKGROUND

[0002] With the rapid development of rail transit technology, the interior lighting system of a high-speed rail carriage is gradually changing from traditional direct lighting to indirect lighting to improve the visual comfort of passengers and the overall aesthetics of the carriage space. Indirect lighting projects light onto the roof or side walls of the carriage, and then forms soft ambient light through reflection of these surfaces, which can effectively avoid the glare problem caused by direct light sources and create a more comfortable riding environment.

[0003] The existing carriage lighting system uses LED light sources with diffuser lampshades to achieve indirect lighting, that is, the diffuser lampshade diffuses the light emitted by the LED to project the light upward onto the roof of the carriage, and the light reflected by the roof forms ambient light, thereby reducing the direct visibility of the light source and achieving an indirect lighting effect with a light utilization rate of about 54%, which improves the glare problem caused by direct lighting.

[0004] Although the diffuser lampshade can achieve soft diffusion of light, in wall washing lighting applications, the wide angle of the light emitted by the LED light source and the lack of secondary optical design result in direct illumination of the light at a wide angle to the wall surface near the lamp, which causes the area to have excessively high illumination. The upper middle area of the wall has insufficient illumination due to a sharp decrease in received light, and the entire illuminated surface exhibits a clear "near-bright far-dark" phenomenon, with an illumination uniformity of only about 0.28, which is much lower than the requirement of 0.6 or more in the standard for high-quality lighting. At the same time, a large amount of light spills into non-target areas to form stray light, which wastes effective luminous flux, and there are problems of uneven illumination distribution, low effective luminous flux utilization, and lack of light direction control. SUMMARY

[0005] To overcome the problems of poor lighting uniformity and low light efficiency, the application provides a design method of a free-form surface optical device for LED indirect lighting on a carriage roof, which designs the free-form surface optical device through mathematical modeling to accurately control the direction of the light emitted by the LED and recombine the light beam, thereby achieving high uniformity and high light efficiency for the lighting on the roof of the carriage.

[0006] Therefore, the first aspect of the embodiment of the present application provides a design method of a free-form optical device for indirect lighting of a vehicle roof LED, comprising: obtaining an installation position and an illumination angle range of an LED light source; calculating a distance interval between the installation position and the vehicle roof; analyzing a light attenuation gradient distribution of the LED light source at different positions on the vehicle roof based on the distance interval and the illumination angle range; obtaining a Euclidean distance of two LED light sources at opposite positions; analyzing an illumination uniformity of the vehicle roof lighting based on the Euclidean distance and the light attenuation gradient distribution; determining a target uniformity according to a preset illumination uniformity standard; obtaining a uniformity difference between the target uniformity and the illumination uniformity; when the uniformity difference is greater than a preset uniformity threshold, reversely calculating a reflection angle required by an outgoing light ray of the LED light source corresponding to each preset sampling point on the vehicle roof based on the target uniformity and the light attenuation gradient distribution; and designing a corresponding free-form surface based on the reflection angle, taking the free-form surface as a reflection surface or a total reflection surface of the free-form optical device.

[0007] As a preferred scheme, the step of obtaining the installation position and the illumination angle range of the LED light source and calculating the distance interval between the installation position and the vehicle roof comprises: obtaining an initial distribution curve of the LED light source; extracting a half peak angle corresponding to a Lambertian light distribution curve of the LED light source from the initial distribution curve as the illumination angle range; collecting a three-dimensional coordinate of the LED light source arranged at a luggage rack of the vehicle cabin towards one end of the vehicle cabin or an edge of the roof as the installation position; and measuring a difference between a vertical coordinate of the installation position and a vertical coordinate of a plane of the vehicle roof as the distance interval.

[0008] As a preferred scheme, the step of analyzing the light attenuation gradient distribution of the LED light source at different positions on the vehicle roof based on the distance interval and the illumination angle range comprises: inputting the distance interval, the illumination angle range and a luminous flux of the LED light source into a preset illuminance calculation model to calculate theoretical illuminance values of a plurality of preset sampling points on the vehicle roof along a light propagation direction; performing normalization processing on the theoretical illuminance values of the plurality of preset sampling points, taking an illuminance value of a sampling point closest to the installation position as a reference value; calculating a ratio of an illuminance value of each sampling point to the reference value, and taking a change rate of the illuminance ratio of two adjacent sampling points as a light attenuation gradient; and collecting all the light attenuation gradients to obtain the light attenuation gradient distribution at different positions on the vehicle roof.

[0009] As a preferred solution, the step of obtaining the Euclidean distance between the two LED light sources, and analyzing the light attenuation gradient distribution based on the Euclidean distance and the light attenuation gradient distribution to analyze the illumination uniformity of the roof lighting of the vehicle cabin comprises: obtaining the installation position coordinates of the two LED light sources symmetrically installed on both sides of the roof rack or the roof edge of the vehicle cabin, and calculating the Euclidean distance between the two installation position coordinates; evenly arranging a plurality of illumination measurement points on the line of the Euclidean distance, and respectively calculating the illumination components received by each illumination measurement point from the two LED light sources according to the light attenuation gradient distribution of each LED light source; superimposing and summing the two illumination components received by each illumination measurement point to obtain the total illumination value of the corresponding measurement point, and traversing all the illumination measurement points to obtain the illumination distribution data of the roof of the vehicle cabin; extracting the minimum illumination value and the average illumination value in the illumination distribution data, and calculating the ratio of the minimum illumination value to the average illumination value as the illumination uniformity of the roof lighting of the vehicle cabin.

[0010] As a preferred solution, the step of calculating the reflection angle required by the light emitted by the LED light source corresponding to each preset sampling point on the roof of the vehicle cabin based on the target uniformity and the light attenuation gradient distribution comprises: inversely calculating the target illumination value required by each preset sampling point on the roof of the vehicle cabin based on the target uniformity; and calculating the reflection angle required by the light emitted by the LED light source corresponding to each preset sampling point based on the target illumination value and the light attenuation gradient distribution according to the cosine law of photometry.

[0011] As a preferred solution, the step of designing a corresponding free-form surface based on the reflection angle comprises: applying the reflection law to calculate point by point to obtain the spatial coordinates of a plurality of reflection points according to a plurality of incident light rays of different angles of the LED light source and the corresponding reflection angles; connecting the spatial coordinates of the plurality of reflection points in order and performing spline interpolation smoothing processing to generate a plurality of direction spline curves; and performing lofting processing and surface fitting on all the direction spline curves to obtain a smooth free-form surface, and taking the smooth free-form surface as a reflection surface or a total reflection surface of a free-form surface optical device.

[0012] As a preferred solution, the step of connecting the spatial coordinates of the plurality of reflection points in order and performing spline interpolation smoothing processing to generate a plurality of direction spline curves comprises: arranging the plurality of reflection points calculated in order according to the incident light ray angles from small to large to obtain a discrete point sequence; performing smoothing processing on the discrete point sequence by using a cubic spline interpolation algorithm or a B-spline curve fitting algorithm to generate a continuous and smooth spline curve; and repeating the above steps in a plurality of different directions to generate a plurality of direction spline curves.

[0013] As a preferred solution, the free-form optical device is in any one of a reflecting cup form or a lens form; when in the reflecting cup form, the smooth free-form surface is used as an inner surface of the reflecting cup; when in the lens form, the smooth free-form surface is used as a total reflection surface of the lens.

[0014] As a preferred solution, when the free-form optical device is in the lens form, the method further comprises: obtaining the refractive index of the lens material and the refractive index of air, calculating a total reflection critical angle; judging whether the incident angle of each light ray of the LED light source incident to the lens surface is greater than the total reflection critical angle; when the incident angle of the LED light source is greater than the total reflection critical angle, the light ray is totally reflected, and the direction of the reflected light ray is calculated by applying the reflection law; when the incident angle of the LED light source is less than or equal to the total reflection critical angle, the light ray is refracted, and the direction of the refracted light ray is calculated by applying the refraction law; and the shape of the lens free-form surface is designed according to the direction of the reflected light ray and the direction of the refracted light ray, so as to ensure that the light rays with large incident angles are guided to the target irradiation area on the top of the vehicle cabin by the lens.

[0015] The technical solution of the present application has the following advantages: by obtaining the installation position and the illumination angle range of the LED light source and calculating the distance interval between the installation position and the top of the vehicle cabin, the geometric relationship between the LED light source and the illuminated surface can be accurately established; by analyzing the distance interval and the illumination angle range, the light attenuation gradient distribution of the LED light source at different positions on the top of the vehicle cabin is analyzed, and the illumination uniformity of the top of the vehicle cabin is analyzed by the Euclidean distance and the light attenuation gradient distribution, so as to quantitatively evaluate the performance of the existing lighting system; according to the preset illumination uniformity standard, the target uniformity is determined and the reflection angle required by the LED exit light ray corresponding to each preset sampling point on the top of the vehicle cabin is reversely calculated, so as to ensure that the designed free-form surface can meet the actual lighting requirements; by designing the corresponding free-form surface according to the reflection angle and using the free-form surface as the reflection surface or the total reflection surface of the free-form optical device, the direction control and beam recombination of the exit light ray of the LED light source can be accurately controlled, the illumination uniformity of the top of the vehicle cabin is improved to more than 0.6, the effective luminous flux utilization rate is greatly improved, the high-quality and uniform lighting effect on the top of the vehicle cabin is realized, and the problems of poor illumination uniformity and low light efficiency in the prior art are overcome. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings required in the following specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 A flowchart of a design method of a free-form optical device for indirect lighting of a LED on a roof of a carriage is provided for an embodiment of the present application.

[0018] Figure 2 A schematic diagram of light rays emitted by a LED light source is provided for an embodiment of the present application.

[0019] Figure 3 A schematic diagram of light rays emitted by a LED light source in a vertical direction is provided for an embodiment of the present application.

[0020] Figure 4 A schematic diagram of light rays emitted by a LED light source in a horizontal direction is provided for an embodiment of the present application.

[0021] Figure 5 A schematic diagram of a structure of a free-form optical device in the form of a lens is provided for an embodiment of the present application.

[0022] Figure 6 A schematic diagram of an effect before optimization of a roof of a carriage is provided.

[0023] Figure 7 A schematic diagram of an effect after optimization of a roof of a carriage is provided.

[0024] Figure 8 A schematic diagram of an effect after optimization of a roof of a carriage is provided.

[0025] Figure 9 A schematic diagram of an effect after optimization of a roof of a carriage is provided. DETAILED DESCRIPTION

[0026] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0027] In the description of the present application, it should be noted that the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0028] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0029] Embodiment 1:

[0030] As Figures 1 to 9As shown, the examples of the present application provide a design method of a free-form optical device for indirect lighting of a vehicle roof by LED, which is used to control the direction of the light emitted by the LED light source used for indirect lighting of the vehicle roof and to recombine the light beam, so as to achieve high uniformity and high light efficiency of the vehicle roof lighting. The design method mainly includes the following steps:

[0031] Step S1, obtain the illumination angle range and installation position of the LED light source, calculate the distance interval between the installation position and the vehicle roof, and analyze the light attenuation gradient distribution of the LED light source at different positions on the vehicle roof based on the distance interval and the illumination angle range.

[0032] Obtain the illumination angle range of the LED light source, and determine the three-dimensional installation position coordinates of the LED light source relative to the vehicle roof plane through measurement or design parameters. Substitute the vertical distance relationship between the illumination angle range of the LED light source and the installation position into the illumination calculation logic, calculate the theoretical illumination variation at different positions on the vehicle roof along the light propagation direction, and thus deduce the light attenuation gradient distribution.

[0033] Wherein, the illumination angle range can be determined by the half peak angle in the initial light distribution curve of the LED; the installation position is expressed by three-dimensional coordinates, which is used to ensure the geometric relationship between the LED light direction and the irradiation area in the subsequent calculation process; the light attenuation gradient distribution is obtained by normalizing the illumination values of a plurality of preset sampling points (the sampling points are distributed along the LED light propagation direction), and the light attenuation gradient is used to represent the slope of the decrease of illumination with the increase of propagation distance.

[0034] In a certain actual vehicle lighting project, the LED light source is installed at a position 180mm away from the vehicle roof, and the half peak angle of the LED is determined to be 60° using the Lambertian light distribution curve of the LED. According to this half peak angle, 20 uniformly distributed sampling points are set in the direction of the center line of the LED emission, and the interval between the sampling points along the irradiation direction is set to 30mm. Then, by inputting the LED light flux, half peak angle and distance parameters into the preset illumination calculation model, the theoretical illumination value of each sampling point is calculated, and the first sampling point is taken as the normalization reference point. Subsequently, the normalized illumination ratio change of the adjacent sampling points is recorded as the light attenuation gradient and a gradient distribution table is formed. The gradient distribution will be used in the subsequent analysis of lighting uniformity and free-form angle inverse calculation.

[0035] Step S2, obtain the Euclidean distance of the two LED light sources at the opposite positions, and analyze the illumination uniformity of the vehicle roof lighting based on the Euclidean distance and the light attenuation gradient distribution.

[0036] The three-dimensional position coordinates of the LED light sources symmetrically installed on both sides of the vehicle compartment need to be obtained, and the Euclidean distance between the two coordinates is calculated. Then, a plurality of illumination measurement points are arranged along the direction of the Euclidean distance line, which are used to simulate the light receiving condition of the vehicle compartment top under the actual lighting scene. Based on the light attenuation gradient distribution obtained in step S1, the illumination contribution values of the two LED light sources to all illumination measurement points are calculated respectively, and then the two contribution values are superimposed to obtain the total illumination of each measurement point. By counting the maximum illumination, minimum illumination and average illumination of all measurement points, the illumination uniformity can be calculated. The illumination uniformity is defined as the ratio of the minimum illumination to the average illumination, and the higher the ratio is, the more uniform the illumination is. By fixing the number of measurement points, the fixed spacing and the fixed measurement line direction, the uniformity calculation can be ensured to be consistent and verifiable under different vehicle models and different lamp layouts.

[0037] If the three-dimensional coordinates of the installation positions of the two LED light sources are (0, 0, 180 mm) and (800 mm, 0, 180 mm) respectively, the Euclidean distance is 800 mm. Forty illumination measurement points are uniformly arranged on the Euclidean distance line, and the spacing between each measurement point is 20 mm. Using the light attenuation gradient distribution obtained in step S1, the illumination values of each measurement point for the left and right LED light sources are calculated respectively. For example, the 15th measurement point is 300 mm away from the left LED horizontally, and according to the light attenuation gradient, the illumination of the left LED to the point is 32 lx, and the illumination of the right LED to the point is 26 lx, so the total illumination of the point is 58 lx. By traversing all measurement points, the illumination distribution data is obtained, such as the minimum illumination is 41 lx, the average illumination is 63 lx, and the illumination uniformity is 0.65.

[0038] Step S3, determine the target uniformity according to the preset lighting uniformity standard, obtain the uniformity difference between the target uniformity and the illumination uniformity, and when the uniformity difference is greater than the preset uniformity threshold, reversely calculate the reflection angle required for the LED light source exit light corresponding to each preset sampling point on the vehicle compartment top based on the target uniformity and the light attenuation gradient distribution.

[0039] The target uniformity value is determined, which is usually based on the vehicle lighting standard, for example, the target uniformity is 0.6 or more. Then, the difference between the current illumination uniformity and the target uniformity is calculated. For example, if the current uniformity is 0.45 and the target uniformity is 0.65, the difference is 0.20. If the difference is greater than the preset threshold (such as 0.05), the direction of the LED exit light needs to be changed through the free-form optical device, so that each sampling point reaches a new target illumination value.

[0040] In the reverse calculation of the reflection angle, the target illumination value of each sampling point needs to be combined with the light attenuation gradient parameter based on the photometric cosine law, to reverse the incident angle of the LED light and the reflection angle after reflection to reach the corresponding position, so as to obtain the reflection angle corresponding to each sampling point.

[0041] For example, if the target uniformity is 0.65 and the current uniformity is only 0.42, the difference is 0.23. At this time, the illumination of the area far from the LED needs to be improved, and the concentrated illumination of the area too close to the LED needs to be reduced. Assuming that the 12th sampling point is expected to be improved to 55lx, and the initial exit angle of the LED is 52°, according to the light attenuation gradient, if 55lx is to be reached, the corresponding LED reflected light must be emitted at about 68°, then the free-form surface needs to form a local slope at this position to realize the reflection angle. By reverse calculating the angle of all sampling points one by one, the reflection angle mapping table of the free-form surface region can be obtained.

[0042] Step S4, based on the reflection angle, design the corresponding free-form surface, and take the free-form surface as the reflecting surface or total reflecting surface of the free-form optical device.

[0043] According to the reflection angle mapping result obtained in step S3, the three-dimensional space coordinates of all reflection points on the free-form surface are calculated point by point in combination with the incident direction of the LED exit light. Subsequently, by sequentially connecting these reflection points, interpolating and smoothing, and fitting the curve, a continuous and optically stable free-form surface structure is constructed. The shape of the free-form surface should meet the requirements of the reflection law and physical manufacturability, such as continuity of the curve, limitation of the machining slope, and no occlusion of the light path. Finally, the fitted free-form surface is applied to the reflector cup structure or lens structure as the key reflecting surface of the optical device, to realize the direction control and uniformization of the LED light beam.

[0044] If the exit direction of the LED light source is set to 0° to 80°, about 50 reflection point coordinate points are calculated according to different angles. These points are arranged in order of incident angle from small to large, and then connected smoothly by cubic spline interpolation, generating multiple direction spline curves. Subsequently, these spline curves are lofted into a curve and fitted in multiple directions to obtain a smooth free-form surface model. After being processed into the reflecting surface of the reflector cup, it is used for actual lamp testing, and the tested illumination uniformity can be improved from the original 0.42 to 0.63.

[0045] In this embodiment, by constructing a geometric optics model with the LED light source illumination angle range, installation position coordinates, and light attenuation gradient distribution as the core, the light propagation law in the indirect lighting scene of the vehicle roof is established. Through step S1, the spatial geometric relationship between the LED light source and the vehicle roof is quantitatively calculated, and the light attenuation results of different areas of the vehicle roof are obtained, providing basic data for subsequent illumination superposition and uniformity evaluation. Then, through step S2, the double light source illumination superposition effect formed by the opposite LED light sources on the vehicle roof is calculated to quantitatively obtain the illumination distribution curve and uniformity index of the vehicle roof, thereby avoiding the defect that the traditional empirical optical design is difficult to intuitively judge the illumination uniformity.

[0046] When the illumination uniformity is insufficient, step S3 uses a reverse calculation method to derive the required reflection angle of each sampling point based on the target uniformity and the light attenuation gradient, so that the lighting design is changed from passive adjustment to active control; this method ensures that the design of the free-form optical device can accurately meet the lighting standards and the target illumination distribution, improving the certainty and controllability of the design. Finally, step S4 converts the reflection angle mapping table into an actual processable free-form surface structure, and constructs a continuous and smooth physical surface through spline interpolation, surface fitting, etc., so that the optical device achieves stable reflection performance. The overall scheme realizes accurate direction control of the LED exit light, significantly improves the uniformity of the vehicle roof lighting, reduces the overflow light, and improves the utilization rate of effective light flux. This embodiment realizes the comprehensive balance of optical performance, manufacturability, and engineering adaptability, effectively solving the problems of uneven illumination and low light efficiency utilization of existing vehicle lighting.

[0047] In another example, step S1 obtains the illumination angle range and installation position of the LED light source, and the step of calculating the distance interval between the installation position and the vehicle roof can be preferably:

[0048] Obtain the initial distribution curve of the LED light source, and extract the half peak angle corresponding to the Lambertian light distribution curve of the LED light source from the initial distribution curve as the illumination angle range.

[0049] As shown in Figure 2 , by importing the initial distribution curve of the LED light source into the optical test software (such as the I(θ) curve generated by the far-field photometric scanner), the angle corresponding to the 50% of the maximum light intensity at which the LED output light intensity drops is located on the curve, that is, the half peak angle. The half peak angle is directly used to define the illumination angle range, thereby ensuring that the LED output light has a real angle boundary condition in the optical design model. In order to ensure the accuracy of the data, the actual test obtained distribution curve should be used instead of the nominal value to avoid errors in subsequent light attenuation gradient calculation; at the same time, the distribution curve needs to be sampled at an angle interval of 1° to ensure that the light intensity drop trend can be accurately captured.

[0050] For example, in a test of an LED module, the maximum luminous intensity of the initial light distribution curve was 980 cd, and the angle reading when the luminous intensity dropped to 490 cd was 57°. Therefore, the illumination angle range can be determined to be 0°~57°. This illumination angle range is used as the limit of the LED emission angle and input into the illuminance calculation model to ensure that subsequent illuminance calculations are consistent with those of actual LED devices.

[0051] The three-dimensional coordinates of the LED light source location are collected at the end of the luggage rack facing the carriage or the edge of the ceiling as the installation position.

[0052] like Figure 3 and Figure 4 As shown, the three-dimensional coordinates of the LED light source installation location are obtained by measuring the reference surface of the internal structure of the carriage. Coordinate acquisition must be based on a fixed reference system (e.g., the center line of the carriage floor as the X-axis, the direction of carriage travel as the Y-axis, and the vertical direction as the Z-axis). To ensure engineering feasibility, the coordinates should include the precise position of the optical center point of the LED light source chip, not the center of the lamp housing. Actual acquisition methods can use a laser rangefinder, a 3D scanner, or structural design parameters, and the coordinates must be recorded in the format (X...). led ,Y led Z led This is to facilitate subsequent modeling of light propagation.

[0053] For example, the optical center coordinates of the LED light source inside the luggage rack of a certain carriage are collected as (X). led =120mm,Y led =–380mm,Z led =1780mm). This coordinate indicates that the LED light source is located at the bottom of the luggage rack on the left side of the carriage, facing the reflective area at the top of the carriage. This coordinate, together with the Z=1980mm plane of the top reflective surface, will form the subsequent distance calculation model.

[0054] The difference between the vertical coordinates of the installation location and the vertical coordinates of the top plane of the carriage is used as the distance spacing.

[0055] like Figure 1 and Figure 6 As shown, by comparing the vertical coordinate Z of the optical center position of the LED light source... led The vertical coordinate Z of the reflective surface on the top of the carriage t This allows us to obtain the vertical distance from the LED light source to the top of the carriage. This distance represents the initial height difference along the light propagation path and is a fundamental parameter for calculating illuminance attenuation. Vertical distance measurements should be taken using a uniform reference surface (e.g., the carriage floor) and the error must be ensured to be no more than ±1mm to avoid significant deviations in light attenuation calculations.

[0056] If the optical center of the LED light source is Z led =1780mm, and the top plane of the carriage Zt =1980mm, then the distance interval is: L=Z t –Z led =200mm This distance will be one of the basic inputs of the illumination calculation model for calculating the illumination variation of different sampling points.

[0057] In another example, the step S1 of analyzing the light attenuation gradient distribution of the LED light source at different positions on the roof of the vehicle cabin based on the distance interval and the lighting angle range can be preferably:

[0058] The distance interval, the lighting angle range, and the luminous flux of the LED light source are input into a preset illumination calculation model to calculate the theoretical illumination values of a plurality of preset sampling points on the roof of the vehicle cabin along the light propagation direction.

[0059] As shown in Figure 7 and Figure 9 , by arranging a plurality of preset sampling points in the LED exit direction, each sampling point has a fixed interval (e.g. 20mm to 30mm), and the theoretical illumination of the point is calculated according to the illumination angle, distance interval and luminous flux parameters.

[0060] The illumination calculation model should be an engineering commonly used model, for example, a distance inverse attenuation model using the cosine law of photometry, the inputs of the model include: LED luminous flux Φ, LED exit angle θ, distance to sampling point d, LED half peak angle limit, whether the light direction is within the effective exit angle, and the output is the theoretical illumination E at the sampling point.

[0061] The LED is set to have a luminous flux Φ=150lm, the lighting angle range is 0°~57°, and 20 sampling points are arranged in the LED exit direction with an interval of 25mm. For the 10th sampling point, the distance to the LED light source center is 250mm, and the incident angle is 40°, then the theoretical illumination can be calculated as:

[0062] E=Φ×cos(θ) / d 2 =150×cos(40°) / (0.25 2 ) The calculation gives E≈176lx.

[0063] The theoretical illumination values of a plurality of preset sampling points are normalized, and the illumination value of the sampling point closest to the installation position is taken as the reference value.

[0064] As shown in Figure 7 , when normalizing the sampling point illumination curve, the illumination of the first sampling point is set to 1.0, and the normalized ratio of other sampling points is obtained by dividing their values by this reference value. Normalization operation facilitates quantification of the speed of illumination decline at different distances, and facilitates comparison between different LED modules. Normalization ensures that subsequent gradient calculation is not affected by absolute luminous flux, but only reflects the natural attenuation law of illumination with distance.

[0065] If the first sampling point illuminance is 280lx and the second is 245lx, the normalized values are: E1=1.0, E2=245 / 280=0.875.

[0066] The ratio of the illuminance value of each sampling point to the reference value is calculated, and the change rate of the illuminance ratio of adjacent sampling points is taken as the light attenuation gradient. All light attenuation gradients are summarized to obtain the light attenuation gradient distribution at different positions on the roof of the vehicle.

[0067] As shown in Figure 7 and Figure 9 , by calculating the difference and trend of the normalized illuminance of adjacent sampling points, the light attenuation gradient can be obtained. For example: G=E (i+1) –E (i) This sequence is used to describe the brightness reduction law during the propagation of LED light, providing a basis for subsequent uniformity analysis.

[0068] If E3=0.82 and E4=0.75, the light attenuation gradient at this point is: G3=0.75–0.82=–0.07.

[0069] In another example, the step S2 obtains the Euclidean distance of the two LED light sources opposite to each other. The step of analyzing the illumination uniformity of the roof lighting based on the Euclidean distance and the light attenuation gradient distribution can be preferably:

[0070] The installation position coordinates of the two LED light sources symmetrically installed on both sides of the luggage rack or the roof edge of the vehicle are obtained, and the Euclidean distance between the two installation position coordinates is calculated.

[0071] As shown in Figure 3 and Figure 4 , by collecting the three-dimensional coordinates (X1, Y1, Z1) and (X2, Y2, Z2) of the two LEDs, the distance between the LEDs is calculated using the Euclidean distance formula: D=√[(X2–X1) 2 +(Y2–Y1) 2 +(Z2–Z1) 2 ] This distance is used to determine the arrangement area and length of the illuminance measurement points.

[0072] The left LED is at (0,–380mm,1780mm) and the right LED is at (800mm,–380mm,1780mm), so the Euclidean distance is 800mm.

[0073] A plurality of illuminance measurement points are uniformly arranged on the line of the Euclidean distance, and the illuminance components received from the two LED light sources are calculated for each illuminance measurement point according to the light attenuation gradient distribution of each LED light source.

[0074] AsFigure 6 and Figure 8 As shown, 40 measurement points are arranged along the line connecting the two LEDs, with a spacing of 20 mm between each point. The distance from each point to the left / right LED and the angle of incidence are calculated. Using the light attenuation gradient in step S1, the corresponding illuminance contribution value can be found.

[0075] For example, measurement point 15 is 300mm from the left LED, corresponding to a normalized illuminance ratio of 0.61, and the corresponding actual illuminance is: E 左 =0.61×E 基准左 E 右 =0.52×E 基准右 .

[0076] The two illuminance components received at each illuminance measurement point are summed to obtain the total illuminance value of the corresponding measurement point. By traversing all illuminance measurement points, the illuminance distribution data of the top of the carriage is obtained.

[0077] like Figure 6 and Figure 8 As shown, the superimposed value represents the final actual brightness at that point. The illuminance distribution curve can be obtained by iterating through all measurement points. For example, E... 15 =E 左 +E 右 =58lx.

[0078] Extract the minimum illuminance value and the average illuminance value from the illuminance distribution data, and calculate the ratio of the minimum illuminance value to the average illuminance value to determine the uniformity of illumination on the roof of the carriage.

[0079] In this step, uniformity = E min / E avg To ensure consistency, no measurement points may be skipped during the calculation process.

[0080] For example, if the minimum illuminance is 41 lx and the average illuminance is 63 lx, then: uniformity = 41 / 63 = 0.65.

[0081] In another example, step S3, which calculates the required reflection angle of the LED light emitted from each preset sampling point on the top of the carriage based on the target uniformity and the light attenuation gradient distribution, can preferably be:

[0082] The target illuminance value required for each preset sampling point on the top of the carriage is calculated based on the target uniformity.

[0083] like Figures 7 to 9 As shown, to achieve the target uniformity of illuminance distribution on the roof of the carriage, after obtaining the current illuminance curve, it is necessary to reverse-engineer the target illuminance that each sampling point should achieve based on the target uniformity value. The reverse calculation process is based on the following logic:

[0084] Target uniformity U t It is a fixed value (e.g., 0.60).

[0085] Assuming average illuminance E avg If kept constant, then the minimum illuminance E min_t =U t ×E avg .

[0086] According to E min_t The requirement is to shift the illuminance curve upwards from the darkest area to meet the uniformity target.

[0087] Based on this, a "target illuminance distribution table" can be constructed to record the required illuminance for each sampling point. This table will serve as input for subsequent back-calculation of the reflection angle.

[0088] To ensure computational feasibility, the target illuminance at all sampling points must correspond one-to-one, with no skipping points or manual interpolation allowed. All values ​​must be calculated based on the light attenuation gradient, sampling point distance, and target uniformity.

[0089] like Figure 8 As shown, the current average illuminance is 63 lx, and the target uniformity is 0.65. Therefore, the minimum target illuminance value is: E min_t =63 × 0.65 = 40.95 lx. If the current illuminance at sampling point 18 is only 36 lx, it needs to be increased to approximately 41 lx; if the current illuminance at sampling point 8 is 55 lx, it needs to be slightly adjusted to 51 lx to make the overall illuminance curve distribution smoother. This method will generate a target illuminance table containing 40 sampling points.

[0090] Based on the photometric cosine law, the required reflection angle of the light emitted from the LED light source at each preset sampling point is calculated according to the target illuminance value and the light attenuation gradient distribution.

[0091] like Figure 2 , Figure 3 , Figure 4 As shown, the target illuminance value at each sampling point is compared with the distance d from the LED light source to that sampling point. i Light attenuation gradient g i Substituting the cosine law of photometry, we can obtain the reflection angle α that the emitted light from the LED must satisfy. i Reflection angle α i The reverse calculation process is based on the following logical chain: the direction of light reflected from the LED after passing through the freeform surface is controllable; the target illuminance value E at each sampling point is... ti Given: optical attenuation gradient g i Given the information, and combining it with the illuminance calculation formula, the angle α can be calculated in reverse. i .

[0092] This step needs to ensure that each sampling point is calculated independently to ensure the continuity and manufacturability of the generated surface.

[0093] As shown in Figure 7 , assuming that the 10th sampling point target illuminance is 52lx, the corresponding light propagation distance is 280mm, and the light attenuation gradient is 0.78, then according to the calculation, the LED exit light needs to be incident on the free-form surface at 63°, and after reflection, it is shot at the sampling point. Similarly, each sampling point is calculated one by one, and 40 reflection angle data points are obtained, forming a "reflection angle mapping table".

[0094] In another example, the step S4 of designing the corresponding free-form surface based on the reflection angle can be preferably:

[0095] According to the multiple different angle incident light of the LED light source and the corresponding reflection angle, the reflection law is applied for point-by-point calculation to obtain the spatial coordinates of multiple reflection points.

[0096] As shown in Figure 5 , there are multiple incident angles between the LED light source and the free-form surface. According to the reflection angle mapping table obtained in step S3, the three-dimensional coordinates of the reflection point that must be formed on the free-form surface are calculated for each incident light (determined by the LED exit angle).

[0097] The calculation must satisfy the following conditions simultaneously: the incident light direction is fixed; the exit light direction is determined by the reflection angle; the reflection surface normal vector n satisfies the reflection law R = I - 2(I·n)n; the reflection point coordinates must be uniquely determined. Each reflection point coordinate can be obtained by solving the spatial reflection geometry equation.

[0098] For example, in the case of LED exit angle of 20° and reflection angle of 55°, the reflection point coordinates (32.5mm, 14.2mm, 1862mm) can be obtained by the reflection equation. For 40 incident lights, 40 reflection point coordinates are obtained, forming a free-form surface discrete point cloud.

[0099] Connect the spatial coordinates of multiple reflection points in order and perform spline interpolation smoothing processing to generate multiple direction spline curves.

[0100] As shown in Figure 5 , to eliminate the breakpoint problem between discrete reflection points, the reflection points need to be sorted (according to the incident angle from small to large) and directionally spline interpolated. The interpolation uses the commonly used cubic spline or B-spline algorithm in engineering optics to generate a smooth curve for subsequent surface lofting.

[0101] Using spline interpolation can ensure that the curve is continuous, smooth, and meets the processability requirements of optical devices (avoiding sudden changes in curvature).

[0102] For example, for 40 reflection points, after sorting by incident angle from 0° to 80°, a cubic spline algorithm is used to fit a curve for every adjacent 3 points, and finally an overall continuous direction spline curve is generated, and three curves are generated in three directions (left-right direction, up-down direction, and tilt direction).

[0103] The lofting processing and surface fitting are performed on all the direction spline curves to obtain a smooth free surface, and the smooth free surface is used as a reflection surface or a total reflection surface of the free-form optical device.

[0104] As shown in Figure 5 , a continuous free surface suitable for physical processing is established by performing a "surface lofting" operation on the plurality of direction spline curves in the three-dimensional space. The surface needs to meet the following requirements: there is no sharp point or sudden change in curvature; no reverse normal vector area is generated; the surface continuity at least reaches the G1 standard; and the position error with the reflection point is not more than ±0.2 mm.

[0105] The free surface obtained after surface fitting can be used for the inner surface of a reflector cup or the total reflection surface structure of a lens.

[0106] 80 spline cross-sectional direction curves participate in lofting, and finally a complete free surface model is formed, with a maximum curvature continuity deviation of 0.12 mm, which meets the optical processing requirements, and the uniformity of illumination is improved from 0.42 to 0.63 in subsequent verification (as Figure 6 and Figure 8 compared).

[0107] The step of sequentially connecting and performing spline interpolation smoothing processing on the spatial coordinates of the plurality of reflection points to generate a plurality of direction spline curves can be preferably as follows:

[0108] The plurality of reflection points calculated are arranged in order of incident light angle from small to large to obtain a discrete point sequence.

[0109] As shown in Figures 3 to 4 , the LED exit angle ranges from 0° to 80°, and N reflection points are calculated. The sorting is used to ensure the consistency of the direction of the curve and avoid crossing or distortion during surface fitting.

[0110] If the LED exit angle is 0°, 10°, 20°, …, 80°, the reflection point sorting is P0, P10, P20, …, P80, a total of 9 points, forming a sequence with consistent direction.

[0111] A cubic spline interpolation algorithm or a B-spline curve fitting algorithm is used to smooth the discrete point sequence to generate a continuous and smooth spline curve.

[0112] AsFigure 5 As shown, interpolation requires the following steps: perform piecewise interpolation on all discrete points; correct the curve endpoints through boundary conditions (zero curvature or specific normal constraints); and ensure the first-order and second-order continuity of the curve.

[0113] For example, after inputting a discrete point sequence, a smooth curve is generated using the cubic spline tool of a certain 3D design software, and the final curve fitting error is less than 0.1 mm.

[0114] Repeat the above steps in multiple planes with different directions to generate multiple directional spline curves.

[0115] In this step, spline curves need to be generated in multiple cross-sections that are transverse, longitudinal, and inclined to the direction of LED emission to ensure that the freeform surface is smooth and continuous in multiple directions at the same time.

[0116] For example, a total of 12 directional spline curves are generated, corresponding to 4 in the vertical direction, 4 in the horizontal direction, and 4 in the inclined direction.

[0117] Furthermore, the freeform surface optical device can be either a reflector cup or a lens. When a reflector cup is used, the smooth freeform surface serves as the inner surface of the reflector cup; when a lens is used, the smooth freeform surface serves as the total internal reflection surface of the lens.

[0118] like Figure 5 As shown, when a freeform surface is used in a reflector structure, its smooth surface directly serves as the reflecting surface; when used in a lens, the surface serves as the total internal reflection interface and must satisfy the total internal reflection condition.

[0119] For example, the reflector cup form is used for aluminum coated reflectors; the lens form is used for PMMA or PC optical lenses.

[0120] Specifically, when the freeform surface optical device takes the form of a lens, the method further includes:

[0121] Obtain the refractive index of the lens material and the refractive index of air, and calculate the critical angle for total internal reflection.

[0122] like Figure 5 As shown, calculating the critical angle requires Snell's law. The refractive index of the lens material, n1 (e.g., 1.49 for PMMA), and the refractive index of air, n2 (1.00), are used to calculate θ. c =arcsin(n2 / n1).

[0123] If n1 = 1.49, then the critical angle θ c =arcsin(1 / 1.49)≈42°.

[0124] determine whether the incident angle of each light ray of the LED light source incident on the surface of the lens is greater than the total reflection critical angle.

[0125] In this step, the incident angle of the light ray θ i is compared with θ c to determine whether the light ray enters the reflection path or the refraction path.

[0126] For example, if the incident angle of a certain incident light ray is 50°, then 50°>42°, so the light ray will execute the total reflection process.

[0127] When the incident angle of the LED light source is greater than the total reflection critical angle, the light ray undergoes total reflection, and the direction of the reflected light ray is calculated using the reflection law.

[0128] For example, if the incident angle of a certain LED light ray is 57°, then the direction of the reflected light ray is calculated according to the reflection law, which is used for subsequent free surface calculation.

[0129] When the incident angle of the LED light source is less than or equal to the total reflection critical angle, the light ray undergoes refraction, and the direction of the refracted light ray is calculated using the refraction law. For example, when the incident angle is 35°≤42°, the refraction angle is calculated to be 23° according to the refraction formula.

[0130] The shape of the lens free surface is designed according to the direction of the reflected light ray and the direction of the refracted light ray, to ensure that the light rays with large incident angles are directed to the target irradiation area on the top of the vehicle cabin through the lens.

[0131] The above embodiments are merely examples for the purpose of clarity, and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. It is not necessary or possible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method of designing a freeform optical device for indirect LED ceiling of vehicle cabin, characterized in that, The method comprises the following steps: obtaining the installation position and the illumination angle range of the LED light source, calculating the distance interval between the installation position and the roof of the vehicle cabin, and analyzing the light attenuation gradient distribution of the LED light source at different positions on the roof of the vehicle cabin based on the distance interval and the illumination angle range; specifically, the distance interval, the illumination angle range and the luminous flux of the LED light source are input into a preset illuminance calculation model to calculate the theoretical illuminance values of a plurality of preset sampling points on the roof of the vehicle cabin along the light propagation direction; normalizing the theoretical illuminance values of the plurality of preset sampling points, and taking the illuminance value of the sampling point closest to the installation position as the reference value; calculating the ratio of the illuminance values of other sampling points to the reference value, and taking the illuminance ratio change rate of adjacent two sampling points as the light attenuation gradient, and collecting all the light attenuation gradients to obtain the light attenuation gradient distribution at different positions on the roof of the vehicle cabin; obtaining the Euclidean distance of the two LED light sources at the opposite positions, and analyzing the illumination uniformity of the roof of the vehicle cabin based on the Euclidean distance and the light attenuation gradient distribution; determining the target uniformity according to the preset illumination uniformity standard, obtaining the uniformity difference between the target uniformity and the illumination uniformity, and when the uniformity difference is greater than the preset uniformity threshold, reversely calculating the reflection angle required for the light emitted by the LED light source corresponding to each preset sampling point on the roof of the vehicle cabin based on the target uniformity and the light attenuation gradient distribution; specifically, the target illuminance value required to be reached by each preset sampling point on the roof of the vehicle cabin is reversely calculated based on the target uniformity; calculating the reflection angle required for the light emitted by the LED light source corresponding to each preset sampling point based on the target illuminance value and the light attenuation gradient distribution according to the cosine law of photometry; designing the corresponding free-form surface based on the reflection angle, taking the free-form surface as the reflecting surface or total reflecting surface of the free-form optical device; specifically, the spatial coordinates of a plurality of reflection points are obtained by point-by-point calculation according to the reflection law based on a plurality of incident light rays of different angles of the LED light source and the corresponding reflection angles; the spatial coordinates of the plurality of reflection points are sequentially connected and subjected to spline interpolation smoothing processing to generate a plurality of directional spline curves; the free-form surface is obtained by lofting processing and surface fitting of all the directional spline curves, and the free-form surface is taken as the reflecting surface or total reflecting surface of the free-form optical device.

2. The method of designing a freeform optical device for LED indirect ceiling of vehicle cabin according to claim 1, wherein, The steps of obtaining the installation position and the illumination angle range of the LED light source, and calculating the distance interval between the installation position and the roof of the vehicle cabin comprise: obtaining the initial distribution curve of the LED light source, and extracting the half peak angle corresponding to the Lambertian light distribution curve of the LED light source from the initial distribution curve as the illumination angle range; collecting the three-dimensional coordinates of the LED light source arranged at the luggage rack of the vehicle cabin towards one end of the vehicle cabin or the edge of the roof as the installation position; measuring the difference between the vertical coordinates of the installation position and the vertical coordinates of the plane of the roof of the vehicle cabin as the distance interval.

3. The method of designing a freeform optical device for LED indirect ceiling of vehicle cabin according to claim 1, wherein, The step of obtaining the Euclidean distance of the two LED light sources opposite to each other based on the Euclidean distance and the light attenuation gradient distribution to analyze the illumination uniformity of the roof lighting of the vehicle compartment comprises: Obtaining the installation position coordinates of the two LED light sources symmetrically installed on both sides of the roof rack or the roof edge of the vehicle compartment, and calculating the Euclidean distance between the two installation position coordinates; Uniformly arranging a plurality of illumination measurement points on the connecting line of the Euclidean distance, and respectively calculating the illumination components received by each illumination measurement point from the two LED light sources according to the light attenuation gradient distribution of each LED light source; Superimposing and summing the two illumination components received by each illumination measurement point to obtain the total illumination value of the corresponding measurement point, and traversing all the illumination measurement points to obtain the illumination distribution data of the roof of the vehicle compartment; Extracting the minimum illumination value and the average illumination value in the illumination distribution data, and calculating the ratio of the minimum illumination value to the average illumination value as the illumination uniformity of the roof lighting of the vehicle compartment.

4. The method of designing a freeform optical device for LED indirect ceiling of vehicle cabin according to claim 1, wherein, The step of connecting the spatial coordinates of the plurality of reflection points in sequence and performing spline interpolation smoothing processing to generate a plurality of directional spline curves comprises: Arranging the plurality of calculated reflection points in order from small to large according to the incident light angle to obtain a discrete point sequence; Using a cubic spline interpolation algorithm or a B-spline curve fitting algorithm to smooth the discrete point sequence to generate a continuous and smooth spline curve; Repeating the above steps in a plurality of different directions to generate a plurality of directional spline curves.

5. The method of designing a freeform optical device for LED indirect ceiling of vehicle cabin according to claim 1, wherein, The free-form optical device is in any one of a reflecting cup form or a lens form; When the reflecting cup form is adopted, the smooth free-form surface is used as the inner surface reflecting surface of the reflecting cup; When the lens form is adopted, the smooth free-form surface is used as the total reflection surface of the lens.

6. The method of designing a freeform optical device for LED indirect ceiling of vehicle cabin according to claim 5, wherein, When the free-form optical device adopts the lens form, the method further comprises: Obtaining the refractive index of the lens material and the refractive index of the air, and calculating the total reflection critical angle; Judging whether the incident angle of each light ray incident to the lens surface of the LED light source is greater than the total reflection critical angle; When the incident angle of the LED light source is greater than the total reflection critical angle, the light ray undergoes total reflection, and the reflection law is applied to calculate the reflection light ray direction; When the incident angle of the LED light source is less than or equal to the total reflection critical angle, the light ray undergoes refraction, and the refraction law is applied to calculate the refracted light ray direction; According to the reflection light ray direction and the refracted light ray direction, the shape of the lens free-form surface is designed to ensure that the high-angle incident light ray is directed to the target illumination area of the roof of the vehicle compartment through the lens. The step of connecting the spatial coordinates of the plurality of reflection points in sequence and performing spline interpolation smoothing processing to generate a plurality of directional spline curves comprises: Arranging the plurality of calculated reflection points in order from small to large according to the incident light angle to obtain a discrete point sequence; Using a cubic spline interpolation algorithm or a B-spline curve fitting algorithm to smooth the discrete point sequence to generate a continuous and smooth spline curve; Repeating the above steps in a plurality of different directions to generate a plurality of directional spline curves. The free-form optical device is in any one of a reflecting cup form or a lens form; When the reflecting cup form is adopted, the smooth free-form surface is used as the inner surface reflecting surface of the reflecting cup; When the lens form is adopted, the smooth free-form surface is used as the total reflection surface of the lens. When the free-form optical device adopts the lens form, the method further comprises: Obtaining the refractive index of the lens material and the refractive index of the air, and calculating the total reflection critical angle; Judging whether the incident angle of each light ray incident to the lens surface of the LED light source is greater than the total reflection critical angle; When the incident angle of the LED light source is greater than the total reflection critical angle, the light ray undergoes total reflection, and the reflection law is applied to calculate the reflection light ray direction; When the incident angle of the LED light source is less than or equal to the total reflection critical angle, the light ray undergoes refraction, and the refraction law is applied to calculate the refracted light ray direction; According to the reflection light ray direction and the refracted light ray direction, the shape of the lens free-form surface is designed to ensure that the high-angle incident light ray is directed to the target illumination area of the roof of the vehicle compartment through the lens.

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